Packages

trait Types extends AnyRef

EXPERIMENTAL

A trait that defines types and operations on them.

Type instances represent information about the type of a corresponding symbol. This includes its members (methods, fields, type parameters, nested classes, traits, etc.) either declared directly or inherited, its base types, its erasure and so on. Types also provide operations to test for type conformance or equivalence or for widening.

To instantiate a type, most of the time, the scala.reflect.api.TypeTags#typeOf method can be used. It takes a type argument and produces a Type instance which represents that argument. For example:

scala> typeOf[List[Int]]
res0: reflect.runtime.universe.Type = scala.List[Int]

In this example, a scala.reflect.api.Types#TypeRef is returned, which corresponds to the type constructor List applied to the type argument Int.

Note: Method typeOf does not work for types with type parameters, such as typeOf[List[A]] where A is a type parameter. In this case, use scala.reflect.api.TypeTags#weakTypeOf instead.

For other ways to instantiate types, see the corresponding section of the Reflection Guide.

Common Operations on Types

Types are typically used for type conformance tests or are queried for declarations of members or inner types.

  • Subtyping Relationships can be tested using <:< and weak_<:<.
  • Type Equality can be checked with =:=. It's important to note that == should not be used to compare types for equality-- == can't check for type equality in the presence of type aliases, while =:= can.

Types can be queried for members and declarations by using the members and declarations methods (along with their singular counterparts member and declaration), which provide the list of definitions associated with that type. For example, to look up the map method of List, one can do:

scala> typeOf[List[_]].member("map": TermName)
res1: reflect.runtime.universe.Symbol = method map

For more information about Types, see the Reflection Guide: Symbols, Trees, and Types

Self Type
Universe
Source
Types.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe
Type Hierarchy
Content Hierarchy
Ordering
  1. Grouped
  2. Alphabetic
  3. By Inheritance
Inherited
  1. Types
  2. AnyRef
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
  1. Hide All
  2. Show All
Visibility
  1. Public
  2. All

Types - Operations

  1. abstract def appliedType(tycon: Universe.Type, args: List[Universe.Type]): Universe.Type

    A creator for type applications

  2. abstract def glb(ts: List[Universe.Type]): Universe.Type

    The greatest lower bound of a list of types, as determined by <:<.

  3. abstract def lub(xs: List[Universe.Type]): Universe.Type

    The least upper bound of a list of types, as determined by <:<.

Types

  1. abstract type AnnotatedType >: Null <: Universe.AnnotatedTypeApi with Universe.Type

    The AnnotatedType type signature is used for annotated types of the for <type> @<annotation>.

  2. abstract type BoundedWildcardType >: Null <: Universe.BoundedWildcardTypeApi with Universe.Type

    BoundedWildcardTypes, used only during type inference, are created in two places:

    BoundedWildcardTypes, used only during type inference, are created in two places:

    1. If the expected type of an expression is an existential type, its hidden symbols are replaced with bounded wildcards. 2. When an implicit conversion is being sought based in part on the name of a method in the converted type, a HasMethodMatching type is created: a MethodType with parameters typed as BoundedWildcardTypes.
  3. abstract type ClassInfoType >: Null <: Universe.ClassInfoTypeApi with Universe.CompoundType

    The ClassInfo type signature is used to define parents and declarations of classes, traits, and objects.

    The ClassInfo type signature is used to define parents and declarations of classes, traits, and objects. If a class, trait, or object C is declared like this

    C extends P_1 with ... with P_m { D_1; ...; D_n}

    its ClassInfo type has the following form:

    ClassInfo(List(P_1, ..., P_m), Scope(D_1, ..., D_n), C)
  4. abstract type CompoundType >: Null <: Universe.CompoundTypeApi with Universe.Type

    A subtype of Type representing refined types as well as ClassInfo signatures.

  5. abstract type ConstantType >: Null <: Universe.ConstantTypeApi with Universe.SingletonType

    The ConstantType type is not directly written in user programs, but arises as the type of a constant.

    The ConstantType type is not directly written in user programs, but arises as the type of a constant. The REPL expresses constant types like Int(11). Here are some constants with their types:

    1           ConstantType(Constant(1))
"abc"       ConstantType(Constant("abc"))
  6. abstract type ExistentialType >: Null <: Universe.ExistentialTypeApi with Universe.Type

    The ExistentialType type signature is used for existential types and wildcard types.

  7. abstract type MethodType >: Null <: Universe.MethodTypeApi with Universe.Type

    The MethodType type signature is used to indicate parameters and result type of a method

  8. abstract type NullaryMethodType >: Null <: Universe.NullaryMethodTypeApi with Universe.Type

    The NullaryMethodType type signature is used for parameterless methods with declarations of the form def foo: T

  9. abstract type PolyType >: Null <: Universe.PolyTypeApi with Universe.Type

    The PolyType type signature is used for polymorphic methods that have at least one type parameter.

  10. abstract type RefinedType >: Null <: Universe.RefinedTypeApi with Universe.CompoundType

    The RefinedType type defines types of any of the forms on the left, with their RefinedType representations to the right.

    The RefinedType type defines types of any of the forms on the left, with their RefinedType representations to the right.

    P_1 with ... with P_m { D_1; ...; D_n}      RefinedType(List(P_1, ..., P_m), Scope(D_1, ..., D_n))
P_1 with ... with P_m                       RefinedType(List(P_1, ..., P_m), Scope())
{ D_1; ...; D_n}                            RefinedType(List(AnyRef), Scope(D_1, ..., D_n))
  11. abstract type SingleType >: Null <: Universe.SingleTypeApi with Universe.SingletonType

    The SingleType type describes types of any of the forms on the left, with their TypeRef representations to the right.

    The SingleType type describes types of any of the forms on the left, with their TypeRef representations to the right.

    (T # x).type             SingleType(T, x)
p.x.type                 SingleType(p.type, x)
x.type                   SingleType(NoPrefix, x)
  12. abstract type SingletonType >: Null <: Universe.SingletonTypeApi with Universe.Type

    The type of Scala singleton types, i.e., types that are inhabited by only one nun-null value.

    The type of Scala singleton types, i.e., types that are inhabited by only one nun-null value. These include types of the forms

    C.this.type
C.super.type
x.type

    as well as constant types.

  13. abstract type SuperType >: Null <: Universe.SuperTypeApi with Universe.SingletonType

    The SuperType type is not directly written, but arises when C.super is used as a prefix in a TypeRef or SingleType.

    The SuperType type is not directly written, but arises when C.super is used as a prefix in a TypeRef or SingleType. It's internal presentation is

    SuperType(thistpe, supertpe)

    Here, thistpe is the type of the corresponding this-type. For instance, in the type arising from C.super, the thistpe part would be ThisType(C). supertpe is the type of the super class referred to by the super.

  14. abstract type ThisType >: Null <: Universe.ThisTypeApi with Universe.SingletonType

    A singleton type that describes types of the form on the left with the corresponding ThisType representation to the right:

    A singleton type that describes types of the form on the left with the corresponding ThisType representation to the right:

    C.this.type             ThisType(C)
  15. abstract type Type >: Null <: Universe.TypeApi

    The type of Scala types, and also Scala type signatures.

    The type of Scala types, and also Scala type signatures. (No difference is internally made between the two).

  16. abstract type TypeBounds >: Null <: Universe.TypeBoundsApi with Universe.Type

    The TypeBounds type signature is used to indicate lower and upper type bounds of type parameters and abstract types.

    The TypeBounds type signature is used to indicate lower and upper type bounds of type parameters and abstract types. It is not a first-class type. If an abstract type or type parameter is declared with any of the forms on the left, its type signature is the TypeBounds type on the right.

    T >: L <: U               TypeBounds(L, U)
T >: L                    TypeBounds(L, Any)
T <: U                    TypeBounds(Nothing, U)
  17. abstract type TypeRef >: Null <: Universe.TypeRefApi with Universe.Type

    The TypeRef type describes types of any of the forms on the left, with their TypeRef representations to the right.

    The TypeRef type describes types of any of the forms on the left, with their TypeRef representations to the right.

    T # C[T_1, ..., T_n]      TypeRef(T, C, List(T_1, ..., T_n))
p.C[T_1, ..., T_n]        TypeRef(p.type, C, List(T_1, ..., T_n))
C[T_1, ..., T_n]          TypeRef(NoPrefix, C, List(T_1, ..., T_n))
T # C                     TypeRef(T, C, Nil)
p.C                       TypeRef(p.type, C, Nil)
C                         TypeRef(NoPrefix, C, Nil)
  1. abstract val NoPrefix: Universe.Type

    This constant is used as a special value denoting the empty prefix in a path dependent type.

    This constant is used as a special value denoting the empty prefix in a path dependent type. For instance x.type is represented as SingleType(NoPrefix, <x>), where <x> stands for the symbol for x.

  2. abstract val NoType: Universe.Type

    This constant is used as a special value that indicates that no meaningful type exists.

  3. abstract val WildcardType: Universe.Type

    An object representing an unknown type, used during type inference.

    An object representing an unknown type, used during type inference. If you see WildcardType outside of inference it is almost certainly a bug.

API

The methods available for each reflection entity, without the implementation. Since the reflection entities are later overridden by runtime reflection and macros, their API counterparts guarantee a minimum set of methods that are implemented.

  1. trait AnnotatedTypeApi extends Universe.TypeApi

    The API that all annotated types support.

    The API that all annotated types support. The main source of information about types is the scala.reflect.api.Types page.

  2. trait BoundedWildcardTypeApi extends Universe.TypeApi

    The API that all this types support.

    The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.

  3. trait ClassInfoTypeApi extends Universe.TypeApi

    The API that all class info types support.

    The API that all class info types support. The main source of information about types is the scala.reflect.api.Types page.

  4. trait CompoundTypeApi extends AnyRef

    Has no special methods.

    Has no special methods. Is here to provides erased identity for CompoundType.

  5. trait ConstantTypeApi extends Universe.TypeApi

    The API that all constant types support.

    The API that all constant types support. The main source of information about types is the scala.reflect.api.Types page.

  6. trait ExistentialTypeApi extends Universe.TypeApi

    The API that all existential types support.

    The API that all existential types support. The main source of information about types is the scala.reflect.api.Types page.

  7. trait MethodTypeApi extends Universe.TypeApi

    The API that all method types support.

    The API that all method types support. The main source of information about types is the scala.reflect.api.Types page.

  8. trait NullaryMethodTypeApi extends Universe.TypeApi

    The API that all nullary method types support.

    The API that all nullary method types support. The main source of information about types is the scala.reflect.api.Types page.

  9. trait PolyTypeApi extends Universe.TypeApi

    The API that all polymorphic types support.

    The API that all polymorphic types support. The main source of information about types is the scala.reflect.api.Types page.

  10. trait RefinedTypeApi extends Universe.TypeApi

    The API that all refined types support.

    The API that all refined types support. The main source of information about types is the scala.reflect.api.Types page.

  11. trait SingleTypeApi extends Universe.TypeApi

    The API that all single types support.

    The API that all single types support. The main source of information about types is the scala.reflect.api.Types page.

  12. trait SingletonTypeApi extends AnyRef

    Has no special methods.

    Has no special methods. Is here to provides erased identity for SingletonType.

  13. trait SuperTypeApi extends Universe.TypeApi

    The API that all super types support.

    The API that all super types support. The main source of information about types is the scala.reflect.api.Types page.

  14. trait ThisTypeApi extends Universe.TypeApi

    The API that all this types support.

    The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.

  15. abstract class TypeApi extends AnyRef

    The API of types.

    The API of types. The main source of information about types is the scala.reflect.api.Types page.

  16. trait TypeBoundsApi extends Universe.TypeApi

    The API that all type bounds support.

    The API that all type bounds support. The main source of information about types is the scala.reflect.api.Types page.

  17. trait TypeRefApi extends Universe.TypeApi

    The API that all type refs support.

    The API that all type refs support. The main source of information about types is the scala.reflect.api.Types page.

Extractors

Extractors provide the machinery necessary to allow pattern matching and construction of reflection entities that is similar to case classes, although the entities are only abstract types that are later overridden.

  1. abstract class AnnotatedTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax AnnotatedType(annotations, underlying).

    An extractor class to create and pattern match with syntax AnnotatedType(annotations, underlying). Here, annotations are the annotations decorating the underlying type underlying. selfSym is a symbol representing the annotated type itself.

  2. abstract class BoundedWildcardTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax BoundedWildcardTypeExtractor(bounds) with bounds denoting the type bounds.

  3. abstract class ClassInfoTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax ClassInfo(parents, decls, clazz) Here, parents is the list of parent types of the class, decls is the scope containing all declarations in the class, and clazz is the symbol of the class itself.

  4. abstract class ConstantTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax ConstantType(constant) Here, constant is the constant value represented by the type.

  5. abstract class ExistentialTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax ExistentialType(quantified, underlying).

    An extractor class to create and pattern match with syntax ExistentialType(quantified, underlying). Here, quantified are the type variables bound by the existential type and underlying is the type that's existentially quantified.

  6. abstract class MethodTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax MethodType(params, restpe) Here, params is a potentially empty list of parameter symbols of the method, and restpe is the result type of the method.

    An extractor class to create and pattern match with syntax MethodType(params, restpe) Here, params is a potentially empty list of parameter symbols of the method, and restpe is the result type of the method. If the method is curried, restpe would be another MethodType. Note: MethodType(Nil, Int) would be the type of a method defined with an empty parameter list.

    def f(): Int

    If the method is completely parameterless, as in

    def f: Int

    its type is a NullaryMethodType.

  7. abstract class NullaryMethodTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax NullaryMethodType(resultType).

    An extractor class to create and pattern match with syntax NullaryMethodType(resultType). Here, resultType is the result type of the parameterless method.

  8. abstract class PolyTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax PolyType(typeParams, resultType).

    An extractor class to create and pattern match with syntax PolyType(typeParams, resultType). Here, typeParams are the type parameters of the method and resultType is the type signature following the type parameters.

  9. abstract class RefinedTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax RefinedType(parents, decls) Here, parents is the list of parent types of the class, and decls is the scope containing all declarations in the class.

  10. abstract class SingleTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax SingleType(pre, sym) Here, pre is the prefix of the single-type, and sym is the stable value symbol referred to by the single-type.

  11. abstract class SuperTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax SingleType(thistpe, supertpe)

  12. abstract class ThisTypeExtractor extends AnyRef

    An extractor class to create and pattern match with syntax ThisType(sym) where sym is the class prefix of the this type.

  13. abstract class TypeBoundsExtractor extends AnyRef

    An extractor class to create and pattern match with syntax TypeBound(lower, upper) Here, lower is the lower bound of the TypeBounds pair, and upper is the upper bound.

  14. abstract class TypeRefExtractor extends AnyRef

    An extractor class to create and pattern match with syntax TypeRef(pre, sym, args) Here, pre is the prefix of the type reference, sym is the symbol referred to by the type reference, and args is a possible empty list of type arguments.

  1. abstract val AnnotatedType: Universe.AnnotatedTypeExtractor

    The constructor/extractor for AnnotatedType instances.

  2. abstract val BoundedWildcardType: Universe.BoundedWildcardTypeExtractor

    The constructor/extractor for BoundedWildcardType instances.

  3. abstract val ClassInfoType: Universe.ClassInfoTypeExtractor

    The constructor/extractor for ClassInfoType instances.

  4. abstract val ConstantType: Universe.ConstantTypeExtractor

    The constructor/extractor for ConstantType instances.

  5. abstract val ExistentialType: Universe.ExistentialTypeExtractor

    The constructor/extractor for ExistentialType instances.

  6. abstract val MethodType: Universe.MethodTypeExtractor

    The constructor/extractor for MethodType instances.

  7. abstract val NullaryMethodType: Universe.NullaryMethodTypeExtractor

    The constructor/extractor for NullaryMethodType instances.

  8. abstract val PolyType: Universe.PolyTypeExtractor

    The constructor/extractor for PolyType instances.

  9. abstract val RefinedType: Universe.RefinedTypeExtractor

    The constructor/extractor for RefinedType instances.

  10. abstract val SingleType: Universe.SingleTypeExtractor

    The constructor/extractor for SingleType instances.

  11. abstract val SuperType: Universe.SuperTypeExtractor

    The constructor/extractor for SuperType instances.

  12. abstract val ThisType: Universe.ThisTypeExtractor

    The constructor/extractor for ThisType instances.

  13. abstract val TypeBounds: Universe.TypeBoundsExtractor

    The constructor/extractor for TypeBounds instances.

  14. abstract val TypeRef: Universe.TypeRefExtractor

    The constructor/extractor for TypeRef instances.

Ungrouped

  1. abstract def appliedType(sym: Universe.Symbol, args: Universe.Type*): Universe.Type

    See also

    appliedType

  2. abstract def appliedType(sym: Universe.Symbol, args: List[Universe.Type]): Universe.Type

    See also

    appliedType

  3. abstract def appliedType(tycon: Universe.Type, args: Universe.Type*): Universe.Type

    See also

    appliedType